This multi-country field study sprayed rice with zinc, iodine, or a cocktail of zinc, iodine, iron and selenium at 21 sites. Untreated brown rice selenium varied more than a hundredfold between sites, and the cocktail containing sodium selenate raised grain selenium about four-fold on average without affecting yield.
Key numbers
- Brown rice selenium with local practice (no foliar selenium): mean 95 µg/kg across 21 site-years, from 3 µg/kg (Patos de Minas, Brazil, 2016) to 404 µg/kg (Ludhiana, India, 2017) (Table 8, p. 9; Results p. 5).
- With the foliar cocktail: mean 380 µg/kg, from 90 µg/kg (Chongqing, China) to 602 µg/kg (Ludhiana, 2017) (Table 8, p. 9).
- The cocktail contained 0.001% sodium selenate (Methods).
- Grain yields were not affected by the foliar treatments (Abstract).
Methods (brief)
Field plots at each site received local control, foliar zinc, foliar iodine, or the micronutrient cocktail. Brown rice was oven-dried and selenium measured by ICP-MS after microwave digestion.
Evidence fitness
Supports the wide natural range of brown rice selenium across rice-growing regions and the effect of foliar selenate. Values are for brown rice from trial plots, not polished or retail rice, and no intake estimates are made.
Limitations
The study was funded by HarvestPlus and the sponsors of a zinc fertilizer project, which include several fertilizer companies; the authors do not report a conflict of interest. Polishing losses were not measured. Replicate counts and detection limits are not restated in the selenium table.
Related evidence
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